Analyses will be carried out, with the use of a data bank of published data sets (more than 250 such sets to date), of changes in DNA base sequence induced by a variety of mutagens, to obtain information on mechanisms of mutagenesis. The data will be interpreted in light of present knowledge of the factors determining mutagenic specificity: formation of mutagenic products in the DNA, repair, and mutagenic processing of lesions during replication. In this work it will be feasible to make comparisons over a wider range of mutagenized genes and cell types than is usually done, and also re-evaluate earlier data in light of more recent results. The agents to be studied include spontaneous processes, ionizing radiation, and oxidizing species such as peroxides and superoxide. Other subjects of study include the formation of frameshifts with associated base change mutations by some mutagens, and the effects of repair on mutagenic specificity. Because of the complexity of the products formed by ionizing radiation, a 1985 review of this subject will be updated. Also, an attempt will be made to develop a better quantitative description of the products formed in intracellular DNA by ionizing radiation, in terms of fractal chemical kinetics.